Particulate filter regeneration in an engine

Abstract

Systems and methods for controlling regeneration of a particulate filter downstream of an engine having a plurality of cylinders are provided. One exemplary method includes, during first conditions, spinning down the engine to non-combusting engine rest, and regenerating the particulate filter at least during engine rest. The method also includes, during second conditions, regenerating the particulate filter during combustion of at least one cylinder of the engine. By regenerating the particulate filter during engine shutdown and/or engine rest in some conditions, it is possible to reduce engine running regeneration, which can thereby lead to reduced engine running emissions.

The invention claimed is: 
     
       1. A method for controlling regeneration of a particulate filter downstream of an engine having cylinders, comprising:
 during first conditions, spinning down the engine to non-combusting engine rest, regenerating the particulate filter during the engine rest by increasing excess oxygen to the particulate filter, including increasing an HP EGR valve opening and closing an engine cylinder; and 
 during second conditions, regenerating the particulate filter during combustion of at least one cylinder of the engine. 
 
     
     
       2. The method of  claim 1 , where, during the first conditions, increasing the excess oxygen further includes increasing a throttle opening. 
     
     
       3. The method of  claim 1 , further comprising, during the first conditions, decreasing a throttle opening and the HP EGR valve opening if excess oxygen at the particulate filter is greater than a high excess oxygen threshold, and increasing the throttle opening and the HP EGR valve opening if the excess oxygen is less than a low excess oxygen threshold. 
     
     
       4. The method of  claim 1 , further comprising, during the second conditions, combusting with an air-fuel ratio about stoichiometry, and increasing excess oxygen by increasing an opening of a ram-air valve in a ram-air conduit. 
     
     
       5. The method of  claim 1 , further comprising, during the first conditions, decreasing a throttle opening if an exhaust temperature is greater than a high temperature threshold, and increasing the throttle opening if the exhaust temperature is less than a low temperature threshold. 
     
     
       6. The method of  claim 1 , further comprising, during the second conditions, retarding spark timing if an exhaust temperature is less than a low temperature threshold, and advancing spark timing if the exhaust temperature is greater than a high temperature threshold. 
     
     
       7. The method of  claim 1 , where an amount of particulate at the particulate filter is less during the first conditions than during the second conditions, and where during the first conditions the particulate filter is regenerated during the engine spin down and during the engine rest. 
     
     
       8. A method for controlling regeneration of a particulate filter downstream of an engine, comprising:
 during combusting engine conditions with an air-fuel ratio about stoichiometry, regenerating a particulate filter downstream of an engine, the regenerating including directing excess oxygen into an exhaust passage upstream of the particulate filter and downstream of a three-way catalyst via intake air boosted by a turbocharger compressor; and 
 after stopping combustion and during engine spin-down, continuing regenerating of the particulate filter. 
 
     
     
       9. The method of  claim 8 , where continuing regenerating of the particulate filter includes directing ram-air into the exhaust passage during vehicle motion. 
     
     
       10. The method of  claim 9 , where one or more of the regenerating and continuing regenerating includes adjusting particulate filter temperature and excess oxygen at the particulate filter by adjusting one or more of ram-air valve opening, throttle opening, spark timing, and engine speed. 
     
     
       11. The method of  claim 8 , where the continuing regenerating includes creating a vacuum in the exhaust passage, and sucking fresh air into the exhaust passage. 
     
     
       12. The method of  claim 8 , where the continuing regenerating includes adjusting an operating parameter to increase or maintain excess oxygen exiting the engine. 
     
     
       13. The method of  claim 12 , where adjusting the operating parameter includes adjusting a throttle opening to increase or maintain excess oxygen exiting the engine. 
     
     
       14. The method of  claim 13 , where adjusting the operating parameter includes adjusting engine speed by controlling an energy conversion device coupled to the engine.